The utility of CVD Al.sub.2 O.sub.3 as a reactive ion etch (RIE) stop layer (during tungsten contact stud patterning) has been clearly demonstrated. For this application, a dense aluminum oxide film is defined as having the following characteristics:
.Index of refraction: 1.59-1.62 PA1 .Etch rate (3.6% phosphoric acid at 75.degree. C.):&lt;25 nm/min PA1 .Hydroxyl content (OH, by infrared (IR) spectroscopy, absorbance per micron of film thickness at 3500 cm-.sup.-1):&lt;0.005 PA1 .Shrinkage of film thickness upon annealing (30 min. at 500.degree. C.):&lt;1.5%
The literature indicates that aluminum tri-isopropoxide (Al(OC.sub.3 H.sub.7)), known in the art as ATI, is a viable sub-500.degree. C. Al.sub.2 O.sub.3 precursor. See, for example, J. A. Aboaf, J. Electrochem. Soc., 114, 948 (1967), J. Fournier et al., Mat. Res. Bull., 23, 31 (1988), J. Kwon, J. Saraie and Y. Yodogawa, J. Electrochem Soc., 132, 890 (1985), H. Mutoh et al., J. Electrochern. Soc., 122, 987 (1975), and R. W. J. Morssinkhof et al., "Mechanistic Aspects of the Deposition of Thin Alumina Films Deposited by MOCVD", paper presented at Spring Meeting of the Materials Research Society, San Francisco, Calif. (1990). In these references, ATI is utilized under conditions in which 1) only bubbling is used to deliver ATI to the reactor, 2) a variety of ATI operating temperatures (78.degree.-170.degree. C.) is practiced, 3) deposition repeatability is not demonstrated, and 4) only a single substrate requires coating. However, while the literature describes the use of ATI for Al.sub.2 O.sub.3 deposition, the literature describes bubbling techniques using an ATI carrier but fails to present a workable manufacturing process. In fact, the bubbling technique described in the literature will not work in a manufacturing environment.
During the aluminum oxide low pressure chemical vapor deposition (LPCVD) process, substrate temperature is critical to the deposition of a high quality aluminum oxide film. Low wafer temperature typically yields a film with high etch rates and low density. If the substrate temperature is not controlled from run to run, the etch rate can vary and subsequent etch processes cannot be accurately controlled in a batch process. Using an embedded thermal measurement device such as a resistance thermal device (RTD) or thermocouple within the susceptor or chuck provides no direct measurement of the wafer/substrate temperature, and there is no guarantee that consecutively processed substrates/wafers will achieve the same temperature and thus the films will have different etch rates. Although the substrate/wafer rests on and may be mechanically gripped by the heated susceptor/chuck, the thermal transfer at process pressure between the substrate/wafer and the susceptor/chuck is not predictable and may lead to large differences between the susceptor/chuck temperature and the successive processed wafers/substrates.
There is no current means to insure wafer/substrate temperature during the LPCVD process. Instead, various external means of calibrating the temperature controller are employed. One such technique requires the process chamber to be vented to atmosphere and a thermocouple probe placed against the wafer susceptor/chuck face to measure the face temperature. Adjustments are then made to the susceptor/chuck temperature controller based on the readings from the thermocouple probe. These types of procedures do not take into account chuck face emissivity, radiation heating effects with the system at process pressure, and/or the wafer/substrate emissivity when the wafer/substrate is place on the chuck/susceptor. The obvious result is a series of "test" runs that are used to measure the etch rate on monitor wafers prior to processing of actual product wafers. This becomes extremely costly with respect to the resource time required, the expense of monitor wafers/substrates, the loss of process tool availability of not only the LPCVD system, but also wet etch and inspection/measurement equipment.
A plasma vapor deposition (sputtered) technique may be employed with several photolithography and wet etch steps to simulate the conformal coverage. However, the many steps increases equipment cost, cycle time, chemical, handling, and additional resources.
An improperly designed delivery system for transporting a low pressure reactive vapor from a heated source vessel to a vacuum processing chamber will lead to vapor decomposition or condensation of the vapor. Either of which result in the reactive vapor byproducts depositing within the delivery system causing restrictions and eventual clogging of the delivery system.
Transporting a low pressure reactive vapor from a heated source vessel to a vacuum processing chamber can lead to decomposition or condensation of the vapor material onto the walls of the supply tubing or flow controlling devices. To initiate and maintain a constant flow of a low pressure vapor material, a heated source vessel is used to provide adequate vapor pressure. An unheated delivery system will allow the vapor to condense within the delivery system causing restrictions and eventual clogging of the delivery system. Conversely, if heating in the delivery system is too high, decomposition of the vapor will occur resulting in poor deposited film quality, inferior etch stop quality within the wafer/substrate, and eventual plating out to form blockages within the delivery system.
Stagnant source chemical trapped in the delivery system during idle periods when there is no flow may also decompose and plate out into the delivery system eventually causing flow restriction and ultimately system blockage. Vacuum pumping of the delivery lines themselves has been demonstrated to be ineffective in removing the reactive source vapor and resultant system blockage. An additional problem can also be encountered due to a surface film being formed in the source vessel that limits the vapor generated and starves the process for reactive chemical. Without correctly designed substrate temperature measurement and control, inert gas purging, and agitation of the source chemical, delivery of the vapor to the process chamber is not a reliable or manufacturable process.